1. Field of the Invention
The present invention is generally related to a system for moderating the temperature of lubricating oil, between low and high limits, for an internal combustion engine and, more particularly, a system which improves the flow of coolant in thermal communication with an oil pan in a marine propulsion system.
2. Description of the Prior Art
It is well known that in certain applications, including many types of marine propulsion systems, internal combustion engines must be water cooled. With marine propulsion systems, the internal combustion engine can be cooled by using water that is drawn from a body of water in which the propulsion system is operated. It is also well know that, in marine propulsion systems, hot exhaust gases are typically conducted from the internal combustion engine along a path that passes through the driveshaft housing in proximity with the oil pan of the engine.
In a typical application of an internal combustion engine, such as a four cycle engine, it is necessary to assure that the lubricating oil is not overheated. Under some conditions, the lubricating oil of a four cycle engine can be cooled below desirable operating temperatures. This is most likely in circumstances where the oil pan of the engine is allowed to be placed in direct thermal contact with water drawn from the body of water in which the marine propulsion system is operated. This can occur in at least two ways. First, when a marine vessel is stationary in a body of water, the weight of the engine often lowers the location of the oil pan to a position in which it is placed in close thermal relationship with the body of water. In other situations, the cooling system of the internal combustion engine may draw cold water from the body of water and cause it to flow in thermal communication with the oil pan before the water flows through the cooling passages of the internal combustion engine. If the temperature of the water in the body of water is sufficiently low, it can cool the oil to a temperature below its most advantageous operating temperature. This can raise the viscosity of the oil and possibly cause the lubricating system to operate at less than efficient levels. Furthermore, this condition can cause fuel condensation in the oil reservoir and increase the volume of the oil.
Many different systems have been developed to address the issues of cooling the exhaust conduit of a marine propulsion system, storing lubricating oil in a reservoir, preventing the overheating of the lubricating oil, and directly cooling the exhaust as it emerges from the internal combustion engine.
U.S. Pat. No. 5,487,687, which issued to Idzikowski et al on Jan. 30, 1996, discloses a midsection and cowl assembly for an outboard marine drive. The marine drive has a midsection between the upper power head and the lower gear case and has a removable midsection cowl assembly which includes first and second sections. The midsection housing includes an oil sump in one embodiment and further includes an exhaust passage encircled by cooling water and partially encircled by engine oil for muffling the engine exhaust noise. The midsection housing also has an oil drain arrangement providing complete and clean oil draining while the outboard drive is mounted on a boat and in the water, wherein the operator can change oil without leaving the confines of the boat and entering the water.
U.S. Pat. No. 5,232,387, which issued to Sumigawa on Aug. 3, 1993, describes an exhaust device for a four cycle outboard motor. The arrangement is provided for the lubricating, cooling and exhaust systems of a four cycle outboard watercraft motor. Coolant is drawn from the body of water within which the watercraft is operated for circulation through the engine cooling system. Subsequently, the coolant is brought into proximity with an exhaust pipe which extends downwardly from the engine within the encasing member. After passing downwardly along the exhaust pipe, the coolant is finally directed towards an exhaust gas expansion chamber and a cooling water jacket provided around the expansion chamber. In order to prevent any of the cooling water from splashing back up against an oil reservoir, which is also located within the casing, a cover is provided across the tops of the expansion chamber and its accompanying cooling water jacket. Cooling water or air may fill the voids separating the various components contained within the encasing. The arrangement is particularly effective in preventing the corrosion of the oil reservoir housing due to back splashed coolant when the watercraft is operated in salt water. It cools the components contained within the encasing and it minimizes heat transfers from higher temperature operating components to lower temperature operating components.
U.S. Pat. No. 4,498,875, which issued to Watanabe on Feb. 12, 1985, describes an outboard motor which comprises a water cooled, four cycle internal combustion engine. In each of two embodiments, an arrangement is provided that offers a compact nature and which uses the coolant delivered to the engine for cooling the oil in the oil pan. In addition, an arrangement is provided whereby the exhaust pipe may pass through the oil pan and yet avoid significant heat transfer from the exhaust system to the lubricating system. In each embodiment of the invention, coolant is delivered to this clearance for further cooling the exhaust system. In one embodiment of the invention, an arrangement is provided for limiting the discharge of coolant from the clearance so as to maintain a level of coolant around the exhaust pipe.
U.S. Pat. No. 4,015,429, which issued to Pichl on Apr. 5, 1977, discloses an outboard motor for reducing exhaust gas pollutants. The outboard motor has an engine located above the water level, a lower unit extending downwardly from the engine, and an exhaust gas tube within the lower unit with its lower end positioned below the water level. Laterally enclosing the closing gas tube is a liquid jacket and a heat insulating jacket is positioned between the exhaust gas tube and the liquid jacket for maintaining the temperature of the exhaust gases at a level such that an afterburning of any oil residue in the exhaust gases is achieved before the gases are discharged from the exhaust gas tube.
U.S. Pat. No. 5,704,819, which issued to Isogawa on Jan. 6, 1998, describes an oil pan arrangement for a four cycle outboard motor. The outboard motor has a high performance twin overhead cam four cycle internal combustion engine. The oil reservoir for the engine is disposed in a driveshaft housing below the engine and an oil pump is driven by the lower end of the engine crankshaft for circulating the oil from the oil tank to the engine. The oil supply system for the engine includes a vertically extending main gallery and a drain passage which extend in parallel side-by-side relationship and which are disposed over the oil tank for ease of oil return. The exhaust and cooling system for the engine is configured so as to minimize heat transfer between the exhaust system and the lubricating system and to maintain a compact assembly.
U.S. Pat. No. 5,522,351, which issued to Hudson on Jun. 4, 1996, discloses an internal combustion engine temperature control system. It comprises a liquid to liquid heat exchanger incorporated into the body of an internal combustion engine. A first cooling liquid, such as oil, is circulating through passages in the engine block and along one side of a heat conducting wall integral with the engine block. A second cooling liquid, such as water, is circulated through a cooling water passage adjacent to the heat conducting wall to remove heat from the first cooling liquid. It may also be pumped through other passages within the engine block for the purpose of cooling the engine.
U.S. Pat. No. 5,752,866, which issued to Takahashi et al on May 19, 1998, describes a lubricating and crankcase ventilating system for a four cycle outboard motor. The outboard motor has a high performance V-type twin overhead cam four cycle internal combustion engine. The oil reservoir for the engine is disposed in a driveshaft housing below the engine and an oil pump is driven by the lower end of the engine crankshaft for circulating the oil from the oil tank to the engine. The exhaust and cooling systems for the engine are configured so as to minimize heat transfer between the exhaust system and the lubricating system. They are also configured to maintain a compact assembly. The oil supply system for the engine includes a vertically extending main gallery and a drain passage which extend in parallel side-by-side relationship with each other. They are disposed over the oil tank for ease of oil return.
U.S. Pat. No. 5,778,847, which issued to Takahashi et al on Jul. 14, 1998, discloses a four cycle outboard motor. The oil reservoir for the engine of the outboard motor is disposed in a driveshaft housing below the engine. An oil pump is driven by the engine crankshaft and circulates the oil from the oil tank to the engine. The oil supply system for the engine includes a vertically extending main gallery and a drain passage which extend in parallel side-by-side relationship with each other. The exhaust and cooling system for the engine is configured so as to minimize heat transfer between the exhaust system and the lubricating system and also to maintain a compact assembly.
All of the patents described above are hereby explicitly incorporated by reference in this description.
Many different techniques for cooling lubricating oil are well known to those skilled in the art. However, the known techniques do not address the problem of lubricating oil which can be excessively cooled, either by the engine cooling system or by thermal communication with a body of water, such as a lake, in which the marine propulsion system is used. It would therefore be significantly beneficial if a temperature control system could be provided in which the temperature of the oil reservoir for a marine propulsion device could be maintained within a preselected range that prevents the lubricating oil from either being overheated or overcooled.